The present invention relates to the field of cutting devices, and more particularly to the field of hand-operated scissors and shears, and specifically to the field of scissors and shears having an ergonomic design in which one or more components of the device are adjustable so as to better conform to the configuration of the operator's hand and the desired cutting orientation of the device. In the following text, the term “scissors” will be used to denote both scissors and shears.
Scissors are a device comprising two blades that are connected together such that, when an operator applies manual pressure, the blades slide past each other, producing a shearing action that cuts a material inserted between the blades. The earliest scissors, dating back over 3000 years to ancient Egypt, were of the “spring” design, having two blades connected at the handle by an arcuate strip of metal that keeps the blades apart until manual pressure is applied. The current “cross-bladed” design originated with the Romans about 100 AD. In this form, scissors comprise two blades conjoined at a pivot, with each blade connected via a shank to a ring or loop that accommodates one or more fingers. Mechanically, such scissors constitute a first-class double-lever system, with the pivot acting as the common fulcrum.
Scissors can be configured as either right-handed or left-handed, with one configuration being the mirror-image of the other. When the blades are fully separated, the scissors are said to be in an open position, as opposed to the closed position, in which the blades fully engage each other along their entire length.
For the purpose of establishing terminology and spatial orientation, FIG. 1a illustrates an exemplary pair of right-handed cross-bladed scissors in a perspective view of the closed position. In this illustration, the blades are aligned with the vertical plane. The exemplary scissors comprise a first blade, a second blade, an upper shank, a lower shank, a finger ring, a thumb ring, a pivot, a tang and a thumb stop. The proximal end of the first blade transitions into the upper shank, which in turn transitions into the finger ring, which in turn transitions into the tang. The proximal end of the second blade transitions into the lower shank, which in turn transitions into the thumb ring, which in turn transitions into the thumb stop. The two blades are pivotally connected near their proximal ends by the pivot, which is typically a screw or pin. In the closed position, the thumb stop engages the finger ring or the upper shank, thereby preventing the blades from crossing beyond the fully overlapped position so as to avoid excessive blade wear and/or deformation.
In the exemplary right-handed configuration of FIG. 1a, the index and middle fingers of the operator's right hand rest on the upper shank; the ring finger is inserted into the finger ring; the pinkie finger rests on the tang; and the thumb is inserted into the thumb ring. When the operator's hand is opened, the leverage of the increased separation between the ring finger and thumb causes the first and second blades to diverge in a V-form from the pivot, thus putting the scissors in an open position. When the operator's hand is closed, the leverage of the diminished separation between the ring finger and thumb causes the first and second blades to converge in an I-form at the pivot, thus putting the scissors in a closed position.
FIG. 1b depicts the same exemplary scissors as FIG. 1a, again in a perspective view of the closed position, showing the three axes about which the scissors can rotate. The longitudinal axis extends forward along the line that connects the pivot to the distal tip of the blades. The vertical axis extends upward from the pivot perpendicular to the longitudinal axis in the vertical plane. The horizontal axis extends laterally leftward from the pivot perpendicular to the longitudinal axis in the horizontal plane. For a right-handed pair of scissors, as illustrated in FIG. 1b, the vertical axis is oriented clockwise with respect to the longitudinal axis, while the horizontal axis is oriented counterclockwise with respect to the longitudinal axis. For a left-handed pair of scissors (not shown) the vertical axis would be oriented counterclockwise with respect to the longitudinal axis, while the horizontal axis would be oriented clockwise with respect to the longitudinal axis.
Referring to FIG. 1b, the scissors can rotate in three different planes: about the longitudinal, vertical or horizontal axes. Borrowing the terminology of aeronautics, we can refer to these three types of rotation as “roll”, “yaw” and “pitch”, respectively. Ergonomically efficient scissors, therefore, must be designed so that the anatomy of the human hand and wrist is compatible with controlling the roll, yaw and pitch of the scissors without engendering undue physical strain and/or fatigue. One of the problems in creating such an ergonomic design is the wide variability of human anatomy in terms of the size of individual hands and wrists and the length and spacing of the fingers. Consequently, a pair of scissors that's designed for the average person will prove awkward and even painful to use for many people, with long-term effects such as carpal tunnel syndrome.
Aside from anatomical variability, the uses to which scissors are put will also influence the optimum ergonomic design. In cutting cloth, for example, the scissors are usually held vertically, with the tip pointing away from the operator. In cutting human hair, on the other hand, the scissors may be held vertically, for trimming the temples, or horizontally, for trimming the top of the head, with the tip generally pointing to the left for a right-handed operator. Pet groomers, however, will also need to hold the scissors vertically, with the tip pointing up or down, in order to trim the flanks and legs of the animal. Since the orientation of the hand on the scissors will be different in each of these applications, no single non-adjustable design will be ergonomically optimal for all of them.
The prior art includes a number of designs that are adjustable with respect to one or more parameters. These parameters include:                Thumb offset: the location of the thumb ring with respect to the finger ring;        Thumb/finger ring rotation: to control roll, yaw and pitch; and        Thumb/finger ring size adjustment.        
Several patents provide for a thumb ring that slides along the lower shank of the scissors. The earliest of these dates back to 1923 in the patent of Gosha, U.S. Pat. No. 1,479,908. Later examples are the patents of Dolph, U.S. Pat. No, 2,158,277, Chuba, U.S. Pat. No. 2,744,324, and Pinto, U.S. Pat. No. 4,146,961. None of these provide for size-adjustable thumb or finger rings. Consequently, these designs cannot provide a universally snug fit for the operator's thumb and ring finger, which will diminish efficiency and comfort of use. Nor do these designs provide any means for rotating the thumb and/or finger rings to achieve optimal control over the roll, yaw and pitch of the scissors. Without such rotation features, all rotational movement must be achieved purely by wrist movements. While the anatomy of the wrist comfortably lends itself to rolling rotation, through a range of about 180°, the same is not true of yaw and pitch, which demand awkward twisting of the wrist through a very constrained range of motion.
Pivoting thumb rings of various types are disclosed in the prior art going as far back as 1897, in the Nolen patent, U.S. Pat. No. 590,330. Later examples of pivoting thumb ring designs are the Pracht patent, U.S. Pat. No. 5,109,608 and the Brenton application, US 2005/0204569. But, since none of these provide a means for locking the thumb ring into a fixed pivoted orientation, rotational control of the scissors is unacceptably unstable. In each of these designs, the thumb ring rotates about the vertical axis only, so that there is no means of controlling pitch short of twisting the wrist. These designs also lack a means for adjusting the thumb offset by relocating the thumb ring along the lower shaft of the scissors. They also fail to provide adjustable sizes for either thumb or finger rings.
Pivoting, interchangeable thumb rings of various sizes are taught by the patent of Brenton et al., U.S. Pat. No. 5,469,624. No means for locking the thumb ring into a fixed pivoted orientation is disclosed, however, nor is there a means for relocating the thumb ring along the lower shaft of the scissors. Moreover, the thumb ring rotates about the vertical axis only, so that there is no means of controlling the pitch of the scissors without twisting the wrist.
The patent of Gauvrey, U.S. Pat. No. 4,642,895, discloses a thumb ring mounted on a sleeve that slides along the lower shaft of the scissors. The thumb ring rotates about the vertical axis only, so that there is no means of controlling scissor pitch without twisting the wrist. Since thumb ring rotation is enabled by a bulky ball-and-socket assembly, the thumb ring is displaced too far from the finger ring to provide an ergonomically efficient configuration. The Gauvrey patent also lacks a means of adjusting the diameter of the thumb or finger rings to accommodate anatomical variations.
The patent application of Lauritzen et al., Pub. No. US 2006/0064879, teaches a thumb ring that's integrated with a sleeve which slides along a shortened lower shaft and also rotates around the lower shaft. A ball-and-socket joint connecting the finger ring to a curved upper shaft enables rotation of the finger ring. This design has several disadvantages. The sizes of the thumb ring and finger ring openings are not adjustable. The basic structure of the scissors is radically altered by specifying a short lower shank and a curved upper shank, thereby requiring special fabrication and increased manufacturing expense.
Since the rotation of the thumb ring in the Lauritzen design is about the longitudinal axis only, only roll can be controlled. This is not optimal, since the natural movement of the wrist can effectively control roll through a wide range of about 180°. While the rotatable connector between the upper shank and finger ring provides limited control of pitch and yaw, it does so at the cost of laterally and vertically displacing the finger ring outside the plane of the lower shaft and thumb ring. The lateral displacement of the finger ring adversely affects blade movement by introducing lateral components into the manual force applied to the finger ring. Such lateral force components will tend to compress the blades together, thereby increasing blade wear and deformation over time. The vertical displacement of the finger ring prevents engagement of the finger ring with the lower shaft and/or thumb stop in the closed position, thereby allowing the blades to cross over each other beyond the fully overlapped position, which again will increase long-term blade wear and deformation.
Consequently, there remains a need, as yet unmet by the prior art, for ergonomic scissors that are adjustable with respect to thumb offset, thumb ring rotation, and thumb/finger ring diameter, so as to enable effective control, in conjunction with unstrained wrist movements, of scissor roll, yaw and pitch. As will now be described, the present invention provides a practical, easy-to-use, economical design that incorporates these essential ergonomic adjustments.